This invention relates to fuel gases and more specifically methods and apparatus for the continual monitoring of the heating value of these fuel gases.
The total heating value of a fuel gas is defined generally as the quantity of heat in British Thermal Units (BTUs) released when one standard cubic foot (SCF) of gas is completely oxidized, with both initial and final temperatures of all ingredients at 60.degree. F. Thus, for example, if the gas is a hydrocarbon or a mixture of several hydrocarbons, the products of a complete oxidation with air are carbon dioxide, nitrogen and water vapor; when on SCF of the gas is mixed with sufficient oxygen to completely oxidize the gas, oxidation is carried out, and the products are cooled to 60.degree. F., the total heat given off is the total heating value of the gas, in BTU/SCF.
Total heating value of a fuel gas, defined in this manner, is used extensively by gas utilities as a measure of the quality of a gas as fuel. If the total heating value is higher, fewer cubic feet of gas are needed to provide the same energy or work. Since the use of fuel gas is based on its heating value per unit volume, the charge for the fuel gas is determined on the same basis.
In addition, the proper operation of burners fed by gas is often extremely dependent upon heating value of the fuel gas. Thus it is important to be able to stabilize the heating value of the fuel gas. To do this, utilities need a method for continually monitoring the heating value.
One previous method for determining heating value involved burning the gas in an excess of oxygen, as for example in F. G. Breyer, U.S. Pat. No. 1,205,704, dated Nov. 21, 1916. Another method requires burning the gas in the exact proportion of oxygen which will bring the flame to its maximum temperature, as in W. H. Clingman, Jr., U.S. Pat. No. 3,777,562, dated Dec. 11, 1973. Since both of these methods involve burning of the gas, inlet conditions (i.e., temperature, pressure, etc.) must be carefully maintained in order to yield accurate readings. Small discrepancies in inlet conditions result in large errors in heating value measurement. Expensive equipment is necessary to correct for these small discrepancies.